1. Field of the Invention
This invention relates to new and useful nonaqueous liquid pigment dispersions which are easy to handle and produce thorough and effective colorations within target media, particularly as compared to standard solid pigments or high-viscosity liquid pigment dispersions. More specifically, the present invention relates to liquid pigment dispersions possessing viscosities of at most 5,000 centipoise at standard temperature and pressure. Such a low viscosity is obtained through the addition of relatively low amounts of aprotic viscosity modifiers possessing dipole moments of between about 1.0 and 5.0, or, alternatively, a flash point of between about xe2x88x9220xc2x0 C. and 180xc2x0 C., such as, most preferably, cyclic carbonates. The resultant low-viscosity pigment compositions thus can be incorporated into any standard coloring method utilizing pigments (such as, for example, for polyurethanes, polyolefins, and the like) without the problems associated with traditionally utilized solid or thickened, high viscosity pigment materials. The method of coloring such target media is also encompassed within this invention.
2. Background of the Prior Art
Polyurethane products, such as foams, resins, and the like, have traditionally been colored by pigments, polymeric colorants, and dyes. Generally, these colorations are performed in situ during foam, resin, etc., formation. For instance, polymeric colorants (i.e., polyoxyalkylenated colorants), such as those described in U.S. Pat. No. 4,284,279 to Cross et al., have been introduced within polyol compositions during slabstock foam production. The xe2x80x9ccoloredxe2x80x9d polyol then reacts with an isocyanate composition, in the presence of a catalyst possibly, to form the desired colored foam. Pigments have also been added in the past, most notably in solid, paste, or powder form, to a polyol stream to form the same type of colored foam products. Such compounds are readily available and inexpensive; however, they also exhibit or create problems during handling, mixing (with other pigments to create different shades, for example), and actual incorporation within target media. Furthermore, pigments, being solid in nature, tend to from clumps of solids within target media that leads to aesthetically displeasing consequences or clogging of machinery or instrumentation (such as pumps, valves, injectors, and the like). Additionally, spills are likely (since the powder or solid form of such pigments do not transport easily due to atmospheric conditions and possible air disturbances), and clothes or hand staining by difficult-to-handle pigment compounds is very likely to occur through the utilization of such solid coloring agents. As such, there is a need to improve upon these handling deficiencies of standard solid and powder pigments compounds. Polymeric colorants, being liquid in nature, have proven easier to use in such processes due to facilitation of handling, particularly at industrial levels. Low viscosity dispersions of pigments with low color availability have been developed within this industry as an attempt to alleviate such handling problems (and thus permit utilization of polymeric colorant-like liquid compositions). However, such low viscosity dispersions are not storage stable and have precipitation problems that produce uneven colorations within the final polyurethane product and thus make such dispersions unsuitable for large-scale industrial use as well. Traditionally, a trade-off has been present with pigments: the higher the viscosity of the pigment solution, the better the storage stability; the lower the viscosity, the worse the storage stability. As such, there is a recognized need to provide an improved pigment dispersion that possesses long-term storage stability as well as good colorability of the target polyurethane composition. Furthermore, such dispersions should exhibit the shade general degree of color depth within the target article substrate as a standard pigment provides. To date, there have existed no such needed advancements in this art.
It is therefore an object of this invention to provide a substantially uniform, low viscosity liquid pigment dispersion for ease of handling in large industrial applications. A further object is to provide a liquid pigment dispersion for utilization within a colored foam production process. A further objective of this invention is to provide a storage-stable pigment dispersion that retains the same general color value as the non-dispersed pigment.
Accordingly, this invention is directed to a nonaqueous liquid dispersion comprising at least one pigment and at least one aprotic viscosity modifying compound exhibiting a dipole moment of between about 1.0 and 5.0 or alternatively, a flash point of between about xe2x88x9220xc2x0 C. and 180xc2x0 C. Also encompassed within this invention is a method of producing a colored polyurethane comprising the steps of
(a) providing a polyol composition;
(b) introducing a nonaqueous liquid dispersion comprising at least one pigment and at least one aprotic viscosity modifying compound exhibiting a dipole moment of at least 1.0. into said polyol composition to form a colored polyol composition; and
(c) mixing said colored polyol composition with an isocyanate to form a polyurethane.
The term xe2x80x9cnonaqueousxe2x80x9d denotes a composition into which no water has been specfically introduced. Due to the possibility of atmospheric water being introduced through exposure to a relatively humid environment, this term does not rule out the potential for any water to be present through such a manner. The term xe2x80x9cliquid dispersionxe2x80x9d is intended to encompass any composition which is present in a fluid state (i.e., possessing a viscosity of below about 10,000 centipoise at standard temperature and pressure). The term xe2x80x9caproticxe2x80x9d is well known within the chemical arts and simply means that no protons can be accepted or donated by the specific compound. As such, it is imperative that certain moieties not be present on the intended viscosity modifying compound. Such unwanted moieties include, without limitation, acid groups, hydroxyls, amines, and the like.. However, as noted above, this list is not definitive; any aprotic compound possessing the required dipole moment or flash point is included in this definition.
The dipole moment requirement for the viscosity modifying compound is necessary to provide the desired performance characteristics for the inventive nonaqueous pigment-containing dispersion. It has been found, surprisingly, that the selection of a relatively low dipole moment viscosity modifying compound provides the desired drastic lowering of overall viscosity while simultaneously separating individual pigment particles within solution, and preventing reagglomeration of the same particles. Furthermore, due to the low dipole moment, the corresponding flash point of the viscosity modifying compound is also relatively low in order to permit removal of such a compound upon introduction within a coloring method utilizing relatively low processing temperatures, if desired. Alternatively, such compounds may also react within the target media as well. As such, since the aprotic compound must exhibit a low flash point, and dipole moments have not been recorded for all compounds which may function in this capacity within the inventive dispersions, the viscosity modifying compound may alternatively be defined in relation to its aprotic nature and its flash point. Thus, a flash point of between about xe2x88x9220xc2x0 C. and 180xc2x0 C. is necessary; preferably such a level is between 0xc2x0 C. and 165xc2x0 C.; more preferably from 80xc2x0 C. to about 160xc2x0 C.; most preferably between about 95xc2x0 C. and 145xc2x0 C. Such an aprotic compound thus does not affect any production methods (such as, as merely one example, polyurethane coloring through initial introduction within a polyol composition followed by admixing with an isocyanate; at low heat exposures, the viscosity modifying compound will evaporate from the final composition with relative ease). It is also preferable that the selected aprotic viscosity modifying compound (or compounds) be liquid in nature and exhibit a viscosity of at most 500 centipoise at standard temperature and pressure (i.e., 25xc2x0 C. at 1 atmosphere) as measured by a Brookfield Viscometer. This requirement facilitates handling (particularly in large-scale industrial applications) and more easily permits production of the desired viscosity level for the nonaqueous liquid pigment dispersion itself.
Also determined to be of great importance to the selection of a proper viscosity modifying compound within the inventive nonaqueous liquid pigment dispersion is the molecular weight of such a compound. Due to the low dipole moment (which concerns the low polarity of the compound itself), and/or the low flash point necessary for such a compound, the molecular weight must also be rather low. Thus, a molecular weight of at most 200 is available for the inventive dispersion; preferably, this weight is at most 150; more preferably, at most about 120; and most preferably, between about 85 and 116.
Such an inventive dispersion is preferably storage stable. By this term, it is intended that the inventive dispersion will remain in a fluid state with substantially no precipitation or reagglomeration of pigment for at least 60 days while being continuously exposed to a temperature of at least 50xc2x0 C. Such a test is one manner of reproducing long-term storage conditions and thus is not intended as being the sole limitation of temperature within this invention. One of ordinary skill in this art would appreciate the need to provide a modified test of this nature. Thus, the inventive dispersions must merely exhibit substantially no precipitation and retention of its fluid state (low viscosity) after exposure to high temperature storage for 60 days.
As noted above, the problems associated with pigments on an industrial scale are remedied through the utilization of low viscosity dispersions. Most mechanisms required to incorporate pigments or pigments dispersions within target media (for example, mixheads and/or feed tank pipes for adding pigments within polyurethane foam production methods utilize certain pumps and feed lines that are highly sensitive to pressure provided by high viscosity pigment formulations. With lower and possibly more uniform viscosities between utilized pigment compositions, versatility of colors increases, thereby providing an overall improved ability to produce desirable end products. Such low viscosity may be (and has been) provided through the introduction of a solvent or viscosity modifier at a point in time near to the actual incorporation of the dispersion within the target media (for polyurethane, the addition would take place either within the polyol component or within the isocyanate component; the two components are mixed together with catalysts to form the desired polyurethane foam). However, this late introduction adds to the complexity and potential problems facing the user in producing such dispersions, again, and particularly, at the industrial level. Thus, a storage stable, low viscosity pigment dispersion is highly desired; unfortunately, such dispersions have not been available until this recent development.
The inventive liquid dispersions exhibit a number of surprising characteristics that lend themselves to a suitable inexpensive, yet highly effective coloring formulation, particularly for polyurethanes. Storage stability, without any appreciable precipitation of the pigments from solution, is of utmost importance with such dispersions. The retention of extremely low viscosities, without any noticeable precipitation, over a long duration, thus provides a highly desired, easy-to-handle product. Without intending to be bound to any scientific theory, it is believed that such storage stability is provided through the interaction of the specifically selected aprotic viscosity modifiers with the target pigment particles while in dispersion. Such modifiers appear to reduce the size of any agglomerated pigment particles (from larger clumps to smaller particles), possibly through hydrogen bonding, initially, and subsequently prevent re-agglomeration by apparently surrounding the target small particles. Even upon heat exposure and centrifugation, the viscosity of the inventive dispersion does not appreciably change. Additionally, the polyurethane foams produced with such inventive dispersions do not exhibit any appreciable losses in color or shade depth in comparison with standard non-modified pigment dispersions. Other impressive similarities between such viscosity modified and non-viscosity modified pigment dispersions are discussed in greater detail below. Succinctly, the inventive dispersions provide improved processability over non-modified pigment dispersions, as well as simultaneous storage stability, all without any appreciable loss in performance as compared with the same non-modified pigment dispersions. Such highly unexpected benefits are of enormous importance to improving upon the available process conditions for applications requiring pigment and/or pigment dispersion utilization.
The viscosity modifiers utilized within this invention must thus be able to actually lower the viscosity of the target pigment dispersions, be able to provide retention of such low viscosities upon long-term storage, must not deleteriously affect the coloring ability of the pigments within the target media, most preferably polyurethane, and must be easily removable from the target media or composition utilized to produce or color such target media at a selected time, or, again, must react within such a target media or media-producing or -coloring composition. The above-discussed ability of the viscosity modifiers to reduce and retain small pigment particle size in the dispersion actually appears to provide more effective colorations throughout the target media. Again, without intending to be limited to one specific scientific explanation or theory, it is believed that by reducing particle size in a stable formulation allows for a more even coloring due to the greater uniformity of pigment size and distribution within the target composition or article. Furthermore, the desired viscosity modifiers of the inventive dispersions must not deleteriously affect the actual target media itself. Preferably, the low dipole moment (and thus low flash point) compounds can be easily evaporated from the target media (such as polyurethane) or the composition utilized to produce such target media, or may react within the target media. Alternatively, if evaporation is not followed (since, for example, heat exposure may deleteriously effect the media itself), the selected compounds would actually be capable of reacting within the target media and enhancing, rather than harming, the characteristics of the target media upon introduction within the pigment dispersion.
With all this in mind, it has been found that certain cyclic compounds, namely and preferably carbonates and lactones, provide the necessary characteristics of the inventive pigment dispersion and exhibit the required low dipole moments. Preferably such viscosity modifiers are alkylene carbonates or butyrolactone; most preferably the modifier is selected from propylene carbonate, butyrolactone, and mixtures thereof. Other modifiers which may be present include DMSO (dimethylsulfoxide), valerolactones (both gamma and sigma types), 1,3-dioxolane, caprolactone, tetrahydrofuran, and the like. The extremely low flash points of 1,3-dioxolane and tetrahydrofuran make them less appealing candidates for selection within this invention; however, their viscosity reducing abilities may be utilized in low temperature processes to produce the desired nonaqueous liquid pigment dispersions. The viscosity modifier (or modifiers) may be present in any amount that provides any reduction in viscosity of the target pigment dispersion. Thus, any amount from about 0.01 to about 25% by weight of the total dispersion is possible; preferably, this amount is from about 1 to about 15% by weight; more preferably from about 5 to about 10% by weight.
The use of cyclic carbonates and cyclic lactones in polyurethane chemistry is known. U.S. Pat. No. 3,883,466 describes the use of a cyclic alkylene carbonate as a liquid modifier to moderate the reaction exotherm between the hydroxy component and the polyisocyanate in the production of a rigid, dense rapid-setting polyurethane. U.S. Pat. Nos. 4,709,002 and 4,731,427 describe the use of cyclic alkylene carbonates in the production of rigid RIM polyisocyanurate and urethane-modified polyisocyanurate parts. These two references do not indicate why cyclic alkylene carbonate is used but do suggest that the carbonate can be added to the isocyanate stream in order to reduce its viscosity. U.S. Pat. Nos. 5,028,635 and 5,149,458 report two polyurea-cyclic carbonate RIM systems having improved flow properties. European Patent 0,350,644 and U.S. Pat. No. 5,442,034 report similar applications for cyclic carbonate in RIM elastomers and spray polyurea elastomers, respectively. U.S. Pat. 4,812,523 describes high solids thermosetting coating composition with cyclic carbonates as reactive diluents to reduce viscosity. Cyclic carbonates and cyclic lactones have also been used as viscosity reducing agents in aromatic polyester polyols and polyether polyols (EP 0,276,452). No teachings or fair suggestions exist, however, that cover the incorporation, addition, etc., of such viscosity reducing agents to already liquid pigment dispersions to improve the desired coloring procedures.
Any standard pigment may be utilized within this inventive dispersion. Thus, carbon black, lamp black, titanium dioxide, phthalocyanine, and the like, may be present. Preferably, the pigment exhibits an individual particle size of between about 13 and 75 nanometers (in order to effectuate a reduction to and retention of the lowest possible agglomerate size). More preferably, then the pigment is a carbon black with a particle size of below about 30 nanometers. The preferred pigment may also be admixed with the viscosity modifier as a solution itself; the only requirement is that the overall viscosity of such a pigment solution be reduced upon introduction of the desired modifier. Most preferred are the following specific pigments: Super Black 34-81107 (from Ferro), Black 34-88111 (from Ferro), Ester Black 33-88033 (from Ferro), Carbon Black 1106 (from Rebus), Black 2101 (from Rebus), High Strength Black 2125 (from Rebus), Polyton Black UE-3012 (from Dainippon Ink and Chemicals, Inc.), Union Black 5U-500 (from Union Chemical Ind., Ltd. of Taiwan), Union Black 3U-600, Ester Black ES100 (from PEKA), Pigment Black (from Dong Ryung of South Korea), Lung Black (from Kuang of Taiwan), Green 1750 (from Rebus), and Blue, Green, and Black Pigment Dispersions from Ryvec. Certain pigments exhibit proper viscosity reductions when admixed with certain viscosity modifiers noted within the low dipole moment class of compounds discussed previously. However, not every low dipole moment compound will produce the same type or level of viscosity modification as desired. For instance, some of the listed viscosity modifiers actually increase the pigment dispersion viscosity and thus are not proper selections on a commercial level. However, these compounds are still effective for other types of pigments and thus are included within the class of modifiers as listed above. The proper selection for commercial practice of certain viscosity modifiers in tandem with certain pigment dispersions is a relatively simple procedure. In order to produce a commercially viable inventive nonaqueous liquid pigment dispersions, one of ordinary skill in the art must analyze a physical mixture of the desired pigment and the low dipole moment viscosity modifying compound(s); if the viscosity does not decrease upon the introduction of 15% by weight of the modifier (in comparison with the total weight of the pigment), then the dispersion should not be utilized at the commercial level. Again, this limit on commercial activity solely pertains to that limited area; the inventive dispersions are not limited in scope due to that selection criteria.
Although the inventive dispersions may comprise a formulation of solely pigment (or mixtures of pigments) and viscosity modifier, other constituents may also be present. Such components include, without limitation, solvents, such as water, lower alcohols, methyl ethyl ketone, and the like; other types of colorants, including dyes, polymeric colorants, inks, and the like; hydrotropes; salts; pH modifiers; and surfactants.